Transformation of natural and synthetic estrogens by maize seedlings

In agricultural fields, crop plants may transform or degrade hormonally active compounds in manure used as fertilizer and thereby affect the overall endocrine-disrupting activity of agricultural runoff. This study examined the transformation of two natural steroid estrogens [17β-estradiol (17β-E2) and estrone (E1)] and two synthetic estrogen mimics [zeranol (α-ZAL) and zearalanone (ZAN)] by maize seedlings. Growing whole maize seedlings in hydroponic solutions of target estrogens resulted in both oxidative (i.e., 17β-E2 to E1 and α-ZAL to ZAN) and reductive (i.e., E1 to 17β-E2 and ZAN to α-ZAL) transformations. Although all four estrogens accumulated in maize roots as both parents and products, the shoots contained only 17β-E2 and α-ZAL, regardless of whether they were the parent or the product. Crude plant enzyme extracts led to substantial reductive transformations but created only trace amounts of oxidation products. In contrast, only oxidative transformations occurred in solutions exposed to plant-associated microbes. Thus, the combined effects of plant enzymes and plant-associated microbes account for the reversible transformations observed with whole plants. These effects are expected to generally decrease the overall estrogenicity of runoff from manure-fertilized fields.